The startle reflex.
it just does...A loud noise makes you jumpbecausethere is a part of your ear that helps you to balance and when disrupted you jump
It is the alternator....
The fuel in the cylinders exploding
When lighting strikes it causes a cavity or vacuum in the air the loud noise is caused by the vacuum collapsing. as an example popping a plastic bag cause the same effect.
Wheel bearing
A little kid in the trunk with a hammer
How is that related to gorrilas? A carp and a gorrilla are NOTHING alike
Noise is a movement of the air. An explosion is a rapid expansion of gasses, which causes movement of the air.
Agressive tread, bad alignment
loose belts
I think it's called an engine